Airborne endotoxin, the focus of the proposed research, is associated with certain occupational asthma syndromes and with chronic airflow obstruction. High level endotoxin exposure occurs in a wide range of workplaces including: cotton mills, grain handling and other agricultural workplaces, machining with water based metal-working fluids, industries with recirculating washwater, and in offices or laboratories with contaminated humidifiers. Exposures to endotoxin in recirculating washwater, as a result of water pollution control, and in water based metal-working fluids are increasingly common. Yet, important questions remain regarding the validity of endotoxin exposure measurements, and methods are not standardized. Thus the levels and patterns of endotoxin exposure associated with significant healthy effects have not been well defined, especially in field studies. As a result, NIOSH or ACGIH have recommended FELS or TLVs for endotoxin. In the absence of regulations and uniformly valid guidelines, efforts to control exposure are only episodic and often motivated only by outbreaks of severe illness. To remedy this situation we propose to: 1) analyze endotoxin exposure-response relationships using previously collected and validated endotoxin exposure data, to determine the levels and patterns of exposure associated with acute respiratory symptoms and lung function changes; and 2) validate standard air sampling and Limulus assay methods for endotoxin in a wide range of industrial and agricultural aerosols using 3-hydroxy fatty acids as markers for lipopolysaccharide content and a mammalian bioassay for relevant endotoxin activity.